The phrase "bellied up" is often used to describe something that is no longer functioning or has failed. Antonyms for this phrase would include words like thriving, successful, and prosperous. These words imply that something is thriving and successful, rather than being in a state of failure or disrepair. Some other antonyms for "bellied up" might include words like healthy, thriving, vibrant, and flourishing. Using these types of antonyms can help to create a more positive and optimistic tone in your writing, as they imply that there is potential for growth and success, instead of only focusing on failure and defeat.